This invention relates to a class of metal complexes, the ligands used to prepare these metal complexes and to olefin polymerization catalysts derived therefrom that are particularly suitable for use in a polymerization process for preparing polymers by polymerization of olefins and mixtures of olefins. Surprisingly, the resulting polymers have been found to possess novel rheological properties indicative of the presence of cross-linking therein. Blends of the resulting polymers with conventional olefin polymers are highly useful in the formation of films for packaging and storage applications and in the preparation of fibers.
Metal complexes containing polydentate chelating ligands are well known in the art. Examples include complexes based on acetylacetonate (AcAc), tetramethylethylenediamine, and other polydentate chelating ligands disclosed in WO 98/030612, Chem. Commun., 1998, 849, JACS, 1998, 120, 4049, and elsewhere. Transition metal complexes based on polydentate derivatives of pyridine are disclosed in WO 98/30612. Examples of multidentate, silane containing complexes include, Fryzuk M. D., Can. J. Chem., 1992, vol 70, 2839-2845, Fryzuk, Michael D., et al, Organometallics 1996, No 15, 3329-3336, and WO 99/57159.
Despite advances in the present art, there remains a need for metal complexes having improved catalytic properties. It would be advantageous to be able to produce polyolefins with improved physical properties. It would be especially advantageous to be able to produce polyolefins, particularly homopolymers and copolymers of ethylene having improved melt strength.
According to the present invention there is provided a process for polymerization of addition polymerizable monomers comprising contacting said monomer under addition polymerization condition with a catalyst composition comprising the reaction product or admixture of:
(A) a metal complex corresponding to the formula: 
xe2x80x83where,
Y is a divalent bridging group, preferably, xe2x80x94(CH2)nxe2x80x2xe2x80x94 where nxe2x80x2 is an integer from 1 to 6, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, or xe2x95x90NR1;
R1 and R2 are each occurrence independently selected from alkyl, aryl, hydrogen, aryloxy, arylthio, alkyloxy, or alkylthio, having up to 10 atoms not counting hydrogen;
X is phosphorus, sulfur, nitrogen, or oxygen;
rxe2x80x2 is 1 or 2 to satisfy the valence of X, and when rxe2x80x2 is 2, the group (R2)rxe2x80x2 can optionally be a divalent group that together with X forms a ring, preferably xe2x80x94(CH2)nxe2x80x2xe2x80x94, where nxe2x80x2 is an integer from 1 to 6;
M is a group 4 metal in the +4 oxidation state, or a group 5 metal in the +5 oxidation state;
R is a monovalent ligand group or 2 R groups together are a divalent ligand group; and
r is 3 or 4 depending on the valence of M; and
(B) an activating cocatalyst, wherein the molar ratio of (A) to (B) is from 1:10,000 to 100:1, and recovering the resulting polymeric product.
Within the scope of this invention are the polyolefin products produced by the aforementioned process, or mixtures thereof with additional polymers, especially additional polyolefin polymers. Preferred products are polyolefins having improved melt rheology properties. It is believed such properties are due to the presence of minor quantities of cross-linkages to other polymer molecules. Such cross-linkages are produced in the polymerization process and not attributable to a crosslink generating comonomer, although such comonomer may additionally be present in the reaction if desired. Desirably, the quantity of such cross-linked polymers is on the order of 0.01 to 10 percent, more preferably 0.01 to 1 percent of the polymer molecules. The presence of such cross-linked functionality is evidenced by 13C NMR spectroscopy, by the presence of a peak at approximately 39.5 ppm measured in C6D6 and the substantial absence of ethyl branches.